For more than 40 years, conductivity has been the inline measurement of choice for inferring black liquor/soda losses from brownstock washing. If properly applied, conductivity can provide a benefit in tracking changes in black liquor filtrate concentration. The implied concentration changes in turn can be used to provide feedback for dilution factor or shower flow control on the last stage of a brownstock washing system. A further extrapolation of this application is the correlation (or lack of correlation) of conductivity to soda loss. For each type of conductivity-based application, there are fundamental principles and assumptions that must be understood and managed to achieve the expected outcomes. The fundamentals of conductivity, the application of conductivity to measure black liquor losses during brownstock washing, and laboratory considerations when attempting to correlate inline process conductivity to absolute sodium content are reviewed and investigated. Finally, the operational objectives and measurement alternatives for employing conductivity measurements are discussed.